Amazon is raising the price of its Prime membership monthly plan by nearly 20 percent. The fee of $99 for an annual membership will not change, the company said Friday.

The online retailer had added the monthly payment option about two years ago as a way to hook shoppers — especially during the holiday season — who wanted faster free shipping, but didn't want to commit to an annual fee. The Seattle-based company does not disclose how many Prime members it has.

Besides free two-day shipping, Prime members get other perks, such as access to Amazon's video and music streaming services.

Starting Friday, new monthly members will pay $12.99 a month, up from $10.99. Qualifying college students will pay $6.49 a month, up from $5.49. Amazon.com Inc. said existing monthly members will start paying the higher fees next month.

Amazon said its $5.99-a-month Prime membership for low-income people who receive government assistance is not affected by the price increase. Amazon launched the discounted Prime membership last year for people who have a valid Electronic Benefits Transfer card.